Sometimes ad hominem is warranted

Phil Plait’s got a serious take-down of the recent claim that there’s been a meteorite found that has diatom fossils in it (at Salon).  Plait’s case is along a few lines: (1) that the rock doesn’t look like it’s a meteorite and has no documentation of how it was found or recovered, (2) the diatoms in it seem to be from Earth, like from a riverbed.  But he opens by criticizing the source of the claim.  He says  N. C. Wickramasinghe, the author of the paper reporting the meteorite, “jumps on everything, with little or no evidence, and says it’s from outer space, so I think there’s a case to be made for a bias on his part.”

Plait then turns to forearm against a concern about the present line of argument:

Now, you might accuse me of using an ad hominem, an argument that cast aspersions on the person making the claim, and not attacking the claim itself. I’ll get to the claim in a moment, but sometimes an ad hominem is warranted!

He makes the case with an analogy:

If Jenny McCarthy claimed botox cures autism, again, you might be forgiven for doubting it based on her previous anti-vaccine and other false claims. You still need to examine the claims on their own merits, of course, but: Fool me once, shame on you; fool me twice, shame on me.

But, now, this isn’t an ad hominem, per se, is it?  When the premises are that the person has a bad track record in the area they are reporting in (or in relevantly similar areas), that’s not ad hominem, but a case against their status as an authority.  I suppose that the basic thought is:  arguments against the person are appropriate when they are relevant to whether the conclusion is acceptable.  If we have reason to believe that S is unreliable, that’s a relevant consideration when we’re considering S’s reportage.

So a question to the NS readers:  should we save terms like ad hominem exclusively for the fallaciously irrelevant considerations of a speaker to impugn his/her claims, or can we allow the term to extend to relevant considerations?  I’ve argued that we should have that flexibility with plenty of other forms of argument, even with straw men and the tu quoque.  But ad hominem seems to have exclusively fallacious connotations for me.  Thoughts?

10 thoughts on “Sometimes ad hominem is warranted”

  1. No extension to relevant considerations. It’s a logical fallacy. Expansion of its use into relevant considerations is not like expansion of “apple” to include computing products. The extension is from the territory of morally vicious behavior (the wrong way to get at truth) into the territory of morally virtuous behavior (the right way to get at truth). Apples and oranges. You’re on thin ice for asking the question, Aikin!

  2. So, let me get this straight, Boog. You don’t think that Wickramasinghe’s track record on these issues is a relevant consideration? Or is it that you don’t see this as a legitimate extension of the TERM ad hominem?

  3. First post!

    Your post is a good read, but I think there’s a difference between a logical fallacy and heuristics. Saying “It’s not a meteorite because Wickramasinghe said it was” is a fallacy. Whoever said it does not affect the object’s being a meteorite or not.

    Saying “I doubt the claim that it’s a meteorite because Wickramasinghe said it” is using a heuristic. Based on previous experience, it’s probably not an event worth discussing. Might it be true? Sure. But there are better ways to spend my time than investigating every claim that bad reporters make.

    To directly answer your question, I think that ad hominem should remain a reference to the fallacy only, making Plait’s claim about Wickramasinghe a use of heuristics rather than a fallacy.

  4. Is this a general point about fallacious and non-fallacious schemes or a particular point about ad hominem? If the former, I think the matter is settled and we ought to use the same word. If the latter, then what exempts the ad hom?

  5. Interesting post! I think that there are admissible/valid forms of ad hominem arguments: Exactly when one makes an argument aiming to show that X is not an authority when it comes to questions of y. These arguments, however, have to be separated from questions whether y is true.
    Consider the old chestnut “that Al Gore is wrong about climate change because he flies in a private jet himself” (or something of the sort). What cannot be inferred from making such a claim is that there is no climate change, or that the evidence for climate change is weak. What can be taken from that claim about Al Gore, if it is true that he flies in a private jet, that he might not be the best ambassador for preventing climate change as long as he doesn’t change his preferred means of transport.
    So, in this context, I think it is alright to doubt somebody’s expertise on extraterrestrial things as long as one doesn’t conflate that with the question whether the object actually is extraterrestrial.

    Is that akin to the position you would endorse, Scott?

  6. Both Josh and Richard are right about this. We, I think, agree that Plait’s argument is productive of a relevant consideration — namely, that Wickramasinghe’s track record is something that functions as a defeater for treating him as a reliable source.

    John Casey’s point is one that I’ve endorsed (with him, also) elsewhere, namely, that fallacy forms are just FORMS, and there can be appropriate usages of those forms. That’s what makes them INFORMAL fallacies. John’s holding my feet to the fire here, as if we hold that there are appropriate usages of fallacy forms, then we should accept the notion of a ‘warranted ad hominem’ as one that fits the bill that Josh and Richard have endorsed here.

    BTW, we’ve had a version of this discussion before on the NS. Check out

  7. If Plait had said that the claim that the rock was a meteorite was false based on Wickramasinghe’s bias, then that would be an ad hominem fallacy.

    If Plait had said that the claim that the rock was a meteorite should not be assumed true based on Wickramasinghe’s bias, then that would not be an ad hominem fallacy.

  8. I thought your question was about the term, though it took some re-reading to conclude that. If the inquiry is about someone’s authority, track record is appropriate evidence. Of course, that inquiry (into authority) is morally suspect, too, because it is likely in play for the purpose of arriving at truth (after authority is established). Sometimes, I suppose, the crutch of authority is excused (e.g., in litigation, where the transaction costs of getting at the truth in a wholly responsible manner would be prohibitively high) or even justified (e.g., in battlefield decisions). If your question didn’t seek how we thought the term should be defined, I’m not sure I understand your question.

  9. As far as the term goes, I think Scott is right. The term “Ad Hominem” has a puerly fallacious conotation, which is why Plait has to preface his “Ad Hominem” by basically saying, ‘I know this type of argument is generally wrong, but in THIS case it’s okay.’ What Plait doesn’t see is that his argument agasint Wickramasinghe is not against him as a person but as an authority, which is fine. Plait is trying to justify something that he doesn’t need to justify.

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